Disclosed herein are biobased chlorine dioxide releasing package label/inserts to be used inside a package, the package label/insert containing (a) at least one layer of pectin and citric acid, (b) at least one layer of gelatin and sodium chlorite, (c) optionally at least one barrier layer containing gelatin (without sodium chlorite) between the at least one layer of pectin and citric acid and the at least one layer of gelatin and sodium chlorite, and (d) an adhesive joining said layers, wherein the package label/insert has alternating layers of the at least one layer of pectin and citric acid and the at least one layer of gelatin and sodium chlorite. Also disclosed are methods of killing microorganisms on an item, involving placing the item in a container or in an outer plastic bag containing several individual packages with the package label/insert described herein and activating the package label/insert to cause the citric acid to come into contact with the sodium chlorite to produce ClO2, wherein the package label releases ClO2 at concentrations of about 1.7 to about 19.1 mg/L air (e.g., 1.7 to 19.1 mg/L air).
Fresh produce consumption is associated with foodborne illnesses. Washing fruits and vegetables with aqueous sanitizing solutions, such as chlorine, is currently used by the industry to reduce microorganisms on the surface of these products and improve their safety. However, these sanitizers in solution cannot penetrate inaccessible areas such as pores, channels and crevices where microorganisms are attached (Annous and Burke, J. Food Prot., 78(5):868-872 (2015)) due to the hydrophobicity of these regions and surface tension (Gomez-Lopez, V., et al., Critical Reviews in Food Science and Nutrition, 48(6): 487-495 (2008); Harris, L. J., et al., Comprehensive Reviews in Food Science and Food Safety, p. 78-141 (2003)).
Gaseous chlorine dioxide has the ability to penetrate and inactivate human pathogens attached to hard-to-reach sites on produce surfaces (Annous and Burke, 2015; Han, Y., et al., Food Microbiology, 17(5): 521-533 (2000)). Chlorine dioxide gas is an effective biocide over a wide range of pH from 3 to 8 (Keskinen and Annous, Chlorine Dioxide (Gas) in Nonthermal Processing Technologies for Food, H. Q. Zhang, et al., Editors, 2011, Wiley, p. 359-365). This gas can be generated by the reaction of an acid with sodium chlorite salt in the presence of moisture (Keskinen and Annous 2011; Kuen S. L., et al., Nature and Science, 5(4): 94-99 (2007); Masschelein, W. J., Chlorine Dioxide-Chemistry and Environmental Impact of Oxychlorine Compounds, 1979, Ann Arbor Science Publishers, Inc., Ann Arbor, Mich.). Unlike chlorine, ClO2 does not chlorinate organic compounds to produce carcinogenic trihalomethanes (THMs); nor does it react with ammonia to form chloramines (Keskinen and Annous, 2011); thus making it very attractive for use as an antimicrobial for foods. In 2001, ClO2 received FDA approval for use to reduce or eliminate microorganisms in a wide variety of food products such as fruits and vegetables (Rulis, A. M., Agency response letter GRAS notice no. GRN 0 00062, 2001). Thus the use of ClO2 can provide an additional hurdle to inactivate and/or inhibit the growth of microorganisms, including human pathogens.
However, due to the safety hazards associated with its storage and distribution, ClO2 is usually generated on site upon demand (Keskinen and Annous, 2011). Current on-site ClO2 generation systems include: (1) stand-alone generators (Annous and Burke, 2015; Prodduk et al., 2014), (2) sachets containing the mixed precursors (e.g., acid with sodium chlorite (Rubino et al., 2011, 2014)), or (3) package films impregnated with the precursors (Ray et al., 2013).
Stand-alone generators, which are on/off systems, offer precise control over when and how much gas to generate but are expensive to operate due to high initial investment and continuous service requirements. They are appropriate for large-scale treatments such as gassing large rooms containing large amount of products. Since the risk of post-treatment re-contamination during packaging does exist, the use of an in-package ClO2 source as the primary and/or secondary treatment would serve as an additional hurdle for microorganism to survive within the package.
In contrast to on/off stand-alone generators, mixing ClO2 precursors within a sachet initiates the reaction and continues ClO2 production until all of the reactants are consumed. Sachets with ClO2 precursors can be packaged with target products to provide treatments in situ. However, the ClO2 precursors (acid and sodium chlorite) are usually separated by a thin membrane, increasing the risk of premature reaction prior to use. In addition, chemical contamination of food from possible rupture of the sachet along with consumers' negative perceptions towards sachets of chemicals within packages make this system less effective and less appealing.
Impregnating package films with both precursors eliminates the potential hazard of contaminating the packaged product with ClO2 precursors. However, in this case, ClO2 generation begins when the film is manufactured and both chemicals embedded within the film start reacting. This shortens the film shelf life and the antimicrobial activity decreases with storage of the film, resulting in inconsistent levels of ClO2 produced when the film is used.
An active packaging system capable of generating and releasing ClO2 when needed could overcome these limitations. One way to address these safety and limitation concerns would be to generate this compound using the labels described below, which may be conveniently placed inside packages.
Earlier we demonstrated the technical feasibility of producing synthetic labels containing ethylene vinyl acetate (EVA; 28% vinyl acetate (VA) and citric acid using extrusion techniques (Saade et al., System Feasibility: designing a chlorine dioxide self-releasing package label to improve fresh produce safety part I: Extrusion approach, Innov. Food Sci. Emerg. Technolo., submitted (2017)). These labels could generate and release gaseous ClO2 in response to a controlled activation mechanism that involved spraying the surface of these labels with concentrated sodium chlorite solution followed by applying heat and pressure. Chlorine dioxide was generated from the reaction of citric acid located at the surface of these labels. The ClO2 generated by these EVA labels was between 6 and 42% of the theoretical calculated yields. This suggested that citric acid molecules located in the bulk of the polymer were inaccessible for reaction due to the hydrophobic nature of EVA polymer. EVA labels released gaseous ClO2 ranging between 0.5 and 3.8 mg/L air, achieving up to 2.3 log reductions (complete inactivation) of Salmonella Montevideo G4639 cells on Tryptic Soy Agar plates (Saade et al., 2017).
To overcome this limitation, we have developed the biobased labels described herein to surprisingly achieve more effective and better control of the release of ClO2, which is necessary for matching the microbial kinetic requirement on food surfaces, medical equipment, and other potential applications requiring decontamination within a package/container systems.